Ratchet and pawl stepping mechanism



April 1961 w. A. ROBERTS 2,977,811

RATCHET AND PAWL STEPPING MECHANISM Filed Nov. 24. 1958 IN V EN TOR.

United States Willard A. Roberts, Galion, Ohio, assignor to North Electric Company, Galion, Ohio, a corporation of Ohio Filed Nov. 24, 1958, Ser. .No. 775,878 7 Claims. (Cl. 74142) This invention relates to mechanisms productive of step-by-step motion and particularly to ratchet and pawl means.

The ratchet and pawl means of this invention has particular adaptation and utility in stepping switches for controlling a multitude of input and output contacts useful in programming, sequence control, routining, impulse counting, tallying, memory devices, and similar applications and uses.

In general, the present pawl and ratchet means is directed to improvements in a mechanism wherein a reciprocating member is used to actuate a drive pawl means having engagement with successive teeth of a ratchet wheel, so that movement of the reciprocating member in one direction causes corresponding incremental rotation of the wheel. According to the present invention, an overthrow pawl moves with the drive pawl to resiliently engage the ratchet wheel and prevent its rotating freely beyond preselected limits in the direction of its advancing movement. A third backup pawl is also provided to prevent rotation of the Wheel in a direction opposite to its direction of intended advancement. The need for the three-pawl system arises, in brief, from the tendency of the ratchet wheel to over-rotate under the driving influence of the drive pawl; the wheel and related mechanisms, unless restrained, have sufficient mass to revolve beyond the preselected limit intended at each drive stroke of the drive pawl. The overthrow pawl, therefore, comes into operation in limiting rotation of the ratchet wheel to incremental movements of designated amplitude, while the backup pawl effectively prevents reverse rotation of the ratchet wheel to assist in driving engagement of the drive pawl with successive teeth of the ratchet wheel, as well as the escapement action of the overthrow pawl, as will appear. The resilient nature and engagement action of the overthrow pawl further minimizes vibration and wear of the ratchet wheel, especially wear of its teeth, and, therefore, ultimately accounts for sustained accuracy of operation for the ratchet and pawl mechanism.

The main object of this invention is to provide a new and improved ratchet and pawl mechanism.

A further object of this invention is to provide a new and improved ratchet and pawl mechanism in which three pawl members are associated with a single ratchet wheel to insure positive direction and amplitude of movement in the wheel in response to the periodic application of a driving impulse thereto.

A still further object of this invention is to provide a new and improved ratchet and pawl mechanism, as aforesaid, which has particular utility in preventing overthrow or revolution of a ratchet wheel beyond preselected limits, whereby the same may be driven rapidly in a step-by-step fashion with preselected increments of rotational movement and with positive assurance of preselected accuracy, both as to direction of movement and the extent thereof.

The above and further objects. features and advanatent Cfitice 2,977,81 l Patented Apr. 4, 1961 tages of this invention will appear to those familiar with the art from the following detailed description of a preferred embodiment of its features and concepts as illustrated in the accompanying drawings.

In the drawings:

Figure l is a partial elevational view of the improved ratchet and pawl mechanism of this invention, showing the same in a first condition of operation;

Figure 2 is another partial view in elevation, similar to Figure 1, showing a second operational condition therefor in which the pawls have been conditioned by movement to the left to advance theratchet wheel in a designated direction and with a preselected increment of movement; and

Figure 3 is a top plan view of the assembly illustrated in Figures 1 and 2.

overthrow pawl 12 superposed in spaced parallelism to pawl 11. Lever 10 normally comprises a bell crank and may be initiated in its motion and caused to move to the left, according to arrow A of Figure 1, in response to energization of electro-magnetic means or other suitable devices familiarly employed in the art for this purpose. Movement of the lever 10 to the left, according to arrow A, serves to tension a return spring means, schematically designated at 15, which at release of the electro-magnetic or other initiating force provides quick return movement of the lever 10 to the right, according to arrow B in Figure 2.

Lever 10 moves toward and away from a stop block 16 which is supported on bracket 17 and held for adjust- 10 by clamping screw means 18.

20 thereof engaging the opposing edge 21 of the triangular-shaped block 16 under the influence of the spring means 15. Thusly, block 16 servcs to regulate the throw of lever 10 to the right and thereby also determines limits of the drive stroke for the drive and related overthrow pawls 11 and 12.

The drive 'pawl 11 is disposed substantially tangential to the ratchet wheel; it is fixed at one end to the outer end of the lever arm 10 and particularly to a projecting of one or more escapes to the radially disposed face of eacn succeeding arrow causes the The overthrow pawi 12 also moves with pawl 11 and is formed as a leaf spring member which is positioned in substantially superposed parallelism with the drive This pawl is particularly formed to include an elongated body portion which extends beyond the der 3 pending finger 25 of the drive pawl to terminate in a depending and substantially transversely related arm portion 32. A tooth engaging finger portion 33 is formed on theouter end of arm portion 32 to lie substantially parallel to the inclined face 35 of a tooth 36 on the ratchet wheel. As will be seen in Figure 1, when finger portion 25 of drive pawl 11 is engaged with the bottom or base of a tooth 30, the tooth engagingfinger portion 33 on the overthrow pawl is disposed substantially at right angles to the finger portion 25 and is therefore aligned to engage an inclined face 35 of each tooth'on the ratchet Wheel 28. The relationship and spacing of the tooth engaging portions 25 and 33 a re so determined that, with the drive pawlfinger 25 engaging the base of tooth 30, for instance, finger portion 33 of the overthrow pawl contacts or closely parallels the inclined face 35 of a succeeding tooth 36, spaced two teeth away from tooth 30. Other spacing relationships may be maintained, of course, without departing from the necessary working arrangement and relationship of the two pawls 11 and 12.

The overthrow pawl is biased lightly upwardly to resiliently engage an overlying and rearwardly depending portion 46 of a stop bar 40 provided to limit movement of pawl 12 away from the ratchet wheel. In this condition, end 33 thereon provides positive braking engagement with the inclined face of a ratchet wheel tooth, but only at the end of each drive stroke (to the right as shown) for the drive and overthrow pawls; the latter slides along portion 46 of stop bar 40 as it moves with pawl 11. The braking action of pawl 12 further is capable of regulation by adjusting the position of the U-shaped stop bar 40 on bracket 17 to which it is held by a single screw 41 which is mounted over washer 42 and passed through an adjusting slot 43 in bar 40 to connect with bracket 17. This relationship provides pivotal adjustment of the stop bar 4-0 about the outside diameter of a bearing 58 which journals one end of axle 45 in supporting the ratchet wheel. Limits are imposed on this pivotal motion determined by the length of the slotted opening 43. Thus, pivotal adjustment of bar 40 about axle 45 serves to position the transversely projecting end portion 46 thereof relative to the outer free end of overthrow pawl 12 which ultimately terminates the limit of outward radial flexure for pawl 12, the latter being adapted to maintain sliding contact with portion 46 throughout its reciprocating movement with pawl 11.

With the above-described arrangement, movement of the drive lever to the left prior to each drive stroke of pawl 11 causes the tooth engaging portion 33 of the overthrow pawl to escape a tooth 36 by moving beyond the point or outer end thereof into a position overlying the next succeeding tooth '(see tooth 47 in Figure 2). Thereafter, movement of the ratchet wheel in a clockwise direction beyond its normal driven position, as produced by movement of the drive pawl 11 to the right, will cause the sloping face 48 of the succeeding tooth 47 to engage the underside of the tooth engaging portion 33Yon the overthrow pawl. This effectively arrests further, clockwise or overthrow rotational movement of the ratchet wheel. If there were no tendency for wheel 28 to overthrow, then face 48 would not so engage portion 33. This invention provides effective means coping with the undesired overthrow motion.

Since the depending finger portion 25 of the drive pawl 11 is designed and intended to engage the base of each tooth in the ratchet wheel, it is necessary, as previously mentioned, that the drive pawl 11 be capable of flexing outwardly to escape past the outer end or edge of each teeth. This being so, there is a tendency for the drive pawl to rotate the ratchet wheel in acounterclockwise direction as the same moves to the left over the outer end of each tooth with movement of drive lever 10 to the'left. To effectively prevent such unwanted counterclockwise rotation of the ratchet wheel, a third pawl 50 is provided. Pawl 50 comprises a metal leaf spring member engageable with the teeth of the ratchet wheel 23 and preferably disposed in tangential relation thereto, so that the outermost end of the pawl member may abuttingly engage the substantially radially disposed face of each tooth on the ratchet wheel. To facilitate this action, pawl member 50 is equipped with an offset end portion 51 adapted to extend into the vacant spacing between teeth and thereby align the extreme end wall 52 in abutting relationship with a ratchet wheel tooth (see Figures l and 2). The third pawl member 50 is carried on a suitable support means (not shown) and flexes outwardly to override the teeth of the ratchet wheel as they pass therebeneath when the wheel rotates in a clockwise direction. Reverse rotation of the wheel is effectively prohibited by its interfering engagement with pawl 59, however. Pawl 50, therefore, serves to maintain the ratchet wheel stationary during the movement of the drive pawl 11 to the left, as viewed in Figure 1. This action permits the overthrow pawl to escape past and the driving pawl to travel across theouter ends of their respectively engaged teeth, the driving pawl resiliently hooking over a succeeding tooth for advancing the ratchet wheel clockwise a preselected increment with movement of the drive lever 10 to the right.

Ratchet wheel 28 may be of conventional construction comprising, as shown, a substantially disc-like wheel having a plurality of modified sloping gear teeth about its periphery. The wheel is suitably attached to a mounting member 55 adjacent one end of a rotor shaft 57, the latter having its one end 45 journaled in a sleeve bearing 58 which is supported in the frame 17.

From the foregoing, it will be readily understood that the ratchet wheel and rotor shaft, the latter in a stepping switch normally carrying contact making elements or the like, form an assembly having suificient mass that it tends to rotate in a clockwise direction beyond the position to which it is driven by the drive lever 10 and the drive pawl 11. Such would do so, except for the presence of the overthrow pawl 12. While the overthrow pawl is simultaneously advanced and returned with the I drive pawl 11, its normal function is that of being resiliently engaged by the inclined face of the ratchet wheel teeth to limit overthrow clockwise rotation of the wheel; the same becomes a positive and semi-rigid stop member by reason of its engagement with the overlying portion 46 of the stop bar 40. Pawl 12, therefore, provides a positive system for preventing the overthrow of the ratchet wheel beyond a preselected and designated rotational position at the end of each driving stroke as determined by movement of drive lever 10 and pawl 11 to the right, according to arrow B of Figure 2.

It is also particularly important to recognize that the arrangement hereinabove described utilizes a relatively large contact area between the overthrow pawls tooth engaging portion 33 and the inclined surface of each ratchet tooth, and that pawl 12 is resilient in its engagement with such teeth, producing minimum wear and maximum life for both the ratchet and the overthrow pawl. The drive pawl, of course, intermittently steps the ratchet wheel in a clockwise direction according to the limited stroking movement of the drive lever 10 with its depending finger 25 engaging behind the radially disposed face of each ratchet tooth, while the third or backup pawl 50 holds the wheel against counterclockwise rotation as the drive pawl escapes each tooth.

From the foregoing it will be appreciated and recognized therefore that while I have herein described and shown the features of my improved mechanism as they relate to a preferred embodiment shown in the drawings, nevertheless numerous changes, modifications and substitutions of equivalents may be madein the structure shown and described without materially departing from the spirit and scope of my invention. It is, therefore, not my intention to be limited in the scope of my invention,

except as may appear in the following appended claims.

I claim:

1. In a ratchet and pawl mechanism, a toothed ratchet wheel, a first pawl having means at one end for engaging the teeth of said wheel, a second pawl having an end portion adapted to be engaged by the teeth of said wheel, means commonly connected to said first and second pawls for reciprocating the same substantially tangentially of said wheel, engagement of said first pawl with said teeth serving to drive the wheel according to the movement of said first pawl in one direction, engagement of said second pawl by the teeth of said wheel serving to limit rotation of the latter in said one direction, and a third pawl aligned substantially tangentially of said wheel and having an end portion abuttingly engageable with teeth of said wheel to prevent rotation of the latter in a direction reverse to said one direction.

2. In a ratchet and pawl mechanism, a rotatably mounted ratchet wheel having teeth at its periphery, a drive lever mounted for reciprocation adjacent said wheel, a first pawl member connected to said drive lever and having means for engaging teeth of said wheel, a second pawl member also attached to said driving lever and adapted to resiliently engage teeth of said wheel, said first and second pawl members being engageable with separate teeth of said wheel, movement of said drive lever moving both of said pawl members in like directions substantially tangentially of said wheel with said first pawl member engaging a tooth to rotate said wheel in one direction, and said second pawl member being adjusted to provide a small clearance between the tooth surface in adjacent relation thereto with the drive lever at the far end of the drive stroke, whereby said first pawl and drive lever determine the distance of rotation of the wheel in each operation thereof, and said second pawl is engaged by the teeth of said wheel only to arrest the latter with overthrow thereof beyond the predetermined limit in said one direction as determined by the movement of said first pawl member in said one direction.

3. The combination as set forth in claim 2 including a third pawl member tangentially aligned with the periphery of said ratchet wheel and having means abuttingly engaging each tooth thereon one by one to prevent rotational movement of the ratchet wheel in a direction opposite to that imposed by the driving movement of said first pawl member.

4. In a ratchet and pawl mechanism a ratchet wheel having a toothed periphery, first, second and third pawl members engageable with separated teeth of said ratchet wheel, two of said pawl members being movable with rectilinear reciprocal movement and the third thereof being stationary, drive means for reciprocating said two pawl members substantially tangentially of said wheel with the movement of said two pawl members in one direction serving to cause one pawl member to engage a tooth thereon and rotate the Wheel in one direction for a distance dictated by the rectilinear movement of said one pawl member, the said second pawl being driven by said drive means and periodically being engaged by the teeth of said wheel to arrest the movement of the latter in said one direction, the said third pawl being adapted to abuttingly engage the teeth of said wheel in a manner to effectively prevent its rotation in a direction reversed to said one direction, and a stop bar mounted in overlying, contacting relation with said second pawl to maintain sliding contact therewith throughout its reciprocal rectilinear movement with said first pawl and said drive means.

5. In a ratchet and paw] mechanism, a rotatably mounted ratchet wheel having teeth disposed along the periphery thereof, each of which teeth has a first and a second inclined surface, a drive lever mounted for reciprocation adjacent said wheel, a first pawl member connected to said drive lever and having a driving surface for engaging the first surface of each tooth, the driving surface being substantially parallel to the first surface of each tooth at the time of engagement therewith; a second pawl member also attached to said driving lever which has a surface adapted to resiliently engage the teeth of said wheel, which surface is disposed substantially parallel to the second surface of each tooth at the moment of engagement therewith, movement of said drive lever effecting movement of said pawl members simultaneously to control said first pawl member to engage a tooth and to rotate said wheela predetermined distance in one direction, and said second pawl member being thereafter disposed adjacent a corresponding tooth on said wheel to engage same responsive to movement of the wheel beyond the predetermined distance in said one direction.

6. A ratchet and pawl mechanism as set forth in claim 5 which includes a stop bar disposed in overlying con tacting relation with said second pawl member to limit movement of the second pawl member away from the ratchet wheel with the occurrence of overthrow by said ratchet wheel.

7. A ratchet and pawl mechanism arrangement as set forth in claim 5 which includes a stop bar disposed in overlying contacting relation with said second pawl member to limit movement of the second pawl member away from the ratchet wheel responsive to the occurrence of overthrow of the wheel, and pivotally adjustable mounting means for mounting said stop bar relative to said second pawl member to permit adjustment of the position of the second pawl member relative to the teeth of the wheel engaged thereby.

References Cited in the file of this patent UNITED STATES PATENTS 

